Dispersion-shifted single-mode fiber having low dispersion slope for large capacity transmission

ABSTRACT

The invention relates to a low dispersion slope dispersion-shifted single-mode fiber for large capacity transmission comprising a core and a cladding. Said fiber is characterized in that said core has three to five core segments having different refractive index profiles, and said cladding has four to six cladding segments. The total dispersion slope of said fiber at 1550 nm is less than 0.060 ps/nm 2 ·km, the zero dispersion wavelength is less than 1420 nm, the effective area ranges from 55 μm 2  to 65 μm 2 , and the dispersion in the region of 1530 nm˜1565 nm ranges from 5.0 ps/nm 2 ·km to 12.0 ps/nm 2 ·km. The fiber has low dispersion slope, moderate dispersion, low attenuation, and excellent bend resistance performance. It is suitable for a high-speed (10 Gbits/s and 40 Gbits/s), large capacity, and long distance DWDM system. Therefore, not only the non-linear problem that fazes high-speed communication is solved effectively, but also the DWDM transmission at 10 Gbits/s can be realized within a wider wavelength range. In addition, low dispersion slope is advantageous for comprehensive management of dispersion, so that the requirement for long distance non-electric relay can be fulfilled.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Chinese Application No.03118463.4, filed on Jan. 14, 2003, the contents of which is herebyincorporated in its entirety by reference.

BACKGROUND OF THE INVENTION

[0002] I. Field of the Invention

[0003] The present invention relates to a single-mode fiber designed forlarge capacity transmission system. The fiber has low dispersion slope,moderate dispersion, low attenuation, and excellent bend resistanceperformance. It is suitable for a high speed (10 Gbits/s and 40Gbits/s), large capacity, long distance dense wavelength divisionmultiplex (DWDM) system, and all the S, C, and L bands of the fiber canbe used for DWDM transmission.

[0004] II. Description of the Related Art

[0005] Since the middle of nineties of the twentieth century, along withthe developments of the erbium-doped fiber-amplifier (EDFA) andwavelength division multiplex (WDM) technology, the fiber communicationenters its unprecedented high-speed developing stage. The capacity ofthe fiber communication increases doubly every year. Today, the bit rateof the commercial transmission system reaches 10 Gbits/s, and thecapacity reached 1.6 T. When the transmission rate exceeds 2.5 Gbits/s,and because of the practicability of the EDFA, dispersion, instead ofattenuation, becomes the main limited factor of long distancetransmission. Along with the development of the WDM technology, theinfluence on the system from the non-linear effects (for example,four-wave mixing, self-phase modulation, cross phase modulation, etc.)among the respective wavelengths limits the augment of the systemcapacity. In order to restrain the influence of the non-linearity in theDWDM system, a proper amount of dispersion is necessary in itstransmission band. Therefore, the development of fiber technologytransfers from zero dispersion-shifted fiber to non-zerodispersion-shifted fiber. A number of methods for designing andproducing such fiber have been disclosed, for example, a non-zerodispersion-shifted fiber having larger effective area and method forproducing the same has disclosed in Chinese Patent 98121639.0, suchfiber has been widely used in the construction of communication backbonenetwork. The further growth of transmission capacity impels theconsideration of sufficiently making use of bandwidth resource of fiber.The range of utilizing amplifier has extended from C-band to L-band. Atthe same time the breakthrough in researching new amplifiers that can beused in wider wavelength range has been realized. It has been reportedthat the product of gain and bandwidth of Raman fiber amplifier (RFA)reaches 132 nm now, and a gain of 30 dB in the range of 1480 nm˜1620 nmcan be obtained. The C-band and L-band RFA modules that can be used in40 Gbits/s system are available commercially. However, the zerodispersion point of the current non-zero dispersion-shifted fiber iswithin S-band, so that S-band cannot be used for DWDM transmission. Inaddition, the dispersion slope in C-band and L-band is somewhat great,and its value exceeds 0.08 ps/nm²·km. Thus, when making management ofdispersion using dispersion compensation technique, except in centralwavelength region, the complete compensation cannot be obtained in sideband regions. The wider wavelength region for transmission shall resultin higher residual dispersion in the side band region. This problem doesnot affect greatly a system which transmission rate is less than 10Gbits/s, however, for a 40 Gbits/s high-speed transmission system thatrequires precisely managing dispersion, the high dispersion slopebecomes a serious problem. Therefore, lowering the dispersion slope offiber is required, so as to decrease the difference between thedispersions of long wavelength and short wavelength that increases alongwith the distance, and the bandwidth can be fully utilized. Because thenon-linear effect affects a large capacity high-speed transmissionsystem more intensively, properly increasing the dispersion value offiber is required, so as to restrain the influence from the non-lineareffect. In the application documents of 00806764.3 in Chinese PatentPublication, there is an embodiment in which a triangular profile thathaving a central depression is adopted, its dispersion slope decreasesto 0.073 ps/nm²·km, but the zero dispersion point is 1499 nm, and notshifted out of S-band, and its dispersion slope is still on the highside. A fiber is disclosed in U.S. Pat. No. 6,396,987B 1, its effectivearea is greater than 60 μm², its dispersion slope is less than 0.07ps/nm²·km, its dispersion at 1550 nm ranges from 7 ps/nm·km to 9ps/nm·km, its zero dispersion point is within 1400 nm˜1440 nm, itscutoff wavelength exceeds 1600 nm, and its attenuation at 1550 nm isless than or equals to 0.23 dB/km. In said U.S. patent, the refractiveindex profiles of the core segments are trapezoidal-index profile andstep-index profile having central depression. A step-index profile isalso given in the application documents of 00802639.4 in Chinese PatentPublication, its dispersion at 1550 nm ranges from 7 ps/nm·km to 15ps/nm·km, and its dispersion slope is less than 0.07 ps/nm²·km.

[0006] However, because the fiber section has a fewer number ofsegments, its structure is rather simple, and the parameters forcontrolling the refractive index profiles of the core segments arerelatively fewer, so that to precisely control the parameters of fiberis difficult. Therefore, to equilibrate and control the dispersion,dispersion slope, effective area, and attenuation performances isdifficult. This situation becomes more prominent in the mass production.

[0007] Definitions and Explanations:

[0008] Relative refractive index difference Δ%=[(n_(i) ²−n_(c) ²)/2n_(i)²]×100 in which n_(i) is the refractive index of the i^(th) layer, andn_(c) is the refractive index of the pure silica glass portion of thecladding, it is the reference refractive index in the invention.

[0009] Refractive index profile is defined as the relation of therelative refractive index difference Δ% or relative refractive index ofa selected portion versus its radius.

[0010] Total dispersion is defined as the algebraic sum of waveguidedispersion and material dispersion of the fiber. In the optical fibercommunication field, the total dispersion is chromatic dispersion offiber. Its unit is ps/nm·km

[0011] Dispersion slope represents the dependence of dispersion onwavelength, it is a slope of such a curve that the wavelength is takenas its abscissa, and the dispersion value is taken as its ordinate. Itsunit is ps/nm²·km. In a WDM system, if the transmission path has largedispersion slope, then the difference of dispersion value betweenwavelengths increases, and the transmission performance is deterioratedas a whole.

[0012] Effective area is defined as:

A _(cff)=2π(∫E ² rdr)²/(∫E ⁴ rdr)

[0013] in which the limit of integration is from 0 to ∞, and E iselectric field that relates to propagation.

[0014] DWDM is the abbreviation of dense wavelength division multiplex.

[0015] The bend resistance performance of fiber refers to as theadditional attenuation under specified test condition. The standard testcondition includes winding 100 turns on a reel having a diameter of 75mm and winding one turn on a reel having a diameter of 32 mm. Theprocess is as follows: first testing attenuation of fiber under normaltest condition; then winding the fiber on a reel and testing itsattenuation according to the standard; the difference of these twotested attenuation values is the bend induced additional attention.Generally, the allowable maximum bend induced attenuation takes the bendinduced additional attenuation at 1310 nm as the standard, the unit ofthe bend induced additional attenuation under each test condition is dB.In the present application the method for testing bend inducesadditional attenuation is more rigorous, i.e., testing the additionalattenuations at 1550 nm and 1625 nm under the conditions of winding 100turns on Φ 60 mm reel and winding one turn on 32 mm reel, and taking themaximum value as the final measured result.

SUMMARY OF THE INVENTION

[0016] The technical problem to be settled by the invention is toprovide a non-zero dispersion-shifted single-mode fiber suitable forhigh speed, large capacity transmission system. Said fiber equilibratesthe following key performances for transmission over fiber: dispersion,dispersion slope, effective area, and attenuation performance.Therefore, not only the non-linear problem that fazes high-speedcommunication is solved effectively, but also the DWDM transmissionabove 10 Gbits/s can be realized within a wider wavelength range. Inaddition, low dispersion slope is advantageous for comprehensivemanagement of dispersion, so that the requirement for long distancenon-electric relay can be fulfilled.

[0017] The technical solution for the aforesaid technical problem is asfollows: the fiber comprising a core and a cladding is characterized inthat said core has three to five core segments having differentrefractive index profiles, said cladding has four to six claddingsegments. The total dispersion slope of said fiber at 1550 nm is lessthan 0.060 ps/nm²·km, the zero dispersion wavelength is less than 1420nm, the effective area ranges from 55 μm² to 65 μm², the dispersion inthe region of 1530 nm˜1565 nm ranges from 5.0 ps/nm²·km to 12.0ps/nm²·km.

[0018] In accordance with the aforesaid technical solution, tipically,said core has three core segments having different refractive indexprofiles, and said cladding has four cladding segments. The relativerefractive index difference ΔCore1% of the first core segment of saidcore ranges from 0.35% to 0.9%, the diameter ΦCore1 ranges approximatelyfrom 2.0 μm to 7.0 μm. The relative refractive index difference ΔCore2%of the second core segment Core2 ranges approximately from 0.25% to0.65%, and the diameter ΦCore2 ranges approximately from 3.0 μm to 8.0μm. The relative refractive index difference ΔCore3% of the third coresegment Core3 ranges approximately from 0.1% to 0.4%, and the diameterΦCore3 ranges approximately from 4.0 μm to 10.0 μm. The relativerefractive index difference ΔClad1% of the first cladding segment Clad1ranges approximately from −0.2% to 0.1%, and the diameter ΦClad1 rangesapproximately from 8.0 μm to 16.0 μm. The relative refractive indexdifference ΔClad2% of the second cladding segment Clad2 rangesapproximately from 0.1% to 0.4%, and the diameter ΦClad2 rangesapproximately from 12.0 μm to 25.0 μm. The relative refractive indexdifference ΔClad3% of the third cladding segment Clad3 rangesapproximately from −0.2% to 0.2%, and the diameter ΦClad3 rangesapproximately from 19.0 μm to 30.0 μm. The fourth cladding segment is alayer of pure silica glass, and its refractive index is the refractiveindex of the pure silica glass n_(c).

[0019] As regards the preferable waveguide structure of the fiber of theinvention, both the relative refractive index difference ΔClad1% of thefirst cladding segment Clad1 and the relative refractive indexdifference ΔClad3% of the third cladding segment Clad3 are negative, andthe ranges of the parameters of the respective core segments andcladding segments are the follows: First core segment Core1: ΔCore1% isabout 0.42 ± 0.06 (0.36˜0.48) ΦCore1 is about 4.6 ± 0.7 μm (3.9˜5.3 μm)Second core segment Core2: ΔCore2% is about 0.35 ± 0.08 (0.27˜0.43)ΦCore2 is about 6.0 ± 1.0 μm (5.0˜7.0 μm) Third core segment Core3:ΔCore3% is about 0.28 ± 0.1 (0.18˜0.38) ΦCore3 is about 7.1 ± 1.5 μm(5.6˜8.6 μm) First cladding segment Clad1: ΔClad1% is about −0.08 ± 0.07(−0.01˜−0.15) ΦClad1 is about 12.5 ± 2.0 μm (10.5˜14.5 μm) Secondcladding segment Clad2: ΔClad2% is about 0.18 ± 0.07 (0.11˜0.25) ΦClad2is about 18.1 ± 2.0 μm (16.1˜20.1 μm) Third cladding segment Clad3:ΔClad3% is about −0.08 ± 0.07 (−0.01˜−0.15) ΦClad3 is about 27.0 ± 2.5μm (24.5˜29.5 μm)

[0020] Fourth cladding segment is a layer of pure silica glass, and itsrefractive index is the refractive index of the pure silica glass n_(c).

[0021] The advantageous effects of the invention are, as compared withthe former structure, more waveguide structural parameters of the fiber,for example, ΔCore1%, ΦCore1, ΔCore2%, ΦCore2, ΔCore3%, ΦCore3, and thevalue of power α that determines the refractive index profile of Core1,can be adjusted. Therefore the design of multiple core segments has thecapability of controlling the performances of the fiber more precisely,and the dispersion, dispersion slope, effective area, and attenuationperformances of the fiber can be equilibrated easily.

[0022] By adjusting the refractive index profile of the fiber, therequired values of dispersion, dispersion slope and larger effectivearea can be obtained, and said fiber possesses lower attenuation andexcellent bending performance. According to the invention, the totaldispersion of the fiber at 1550 nm is less than 0.060 ps/nm²·km, thezero-dispersion wavelength is less than 1420 nm, the effective arearanges from 55 μm² to 65 μm², the dispersion in the range of 1530nm˜1565 nm is 5.0˜12.0 ps/nm²·km, the attenuation at 1550 nm is lessthan or equals to 0.22 dB/km. According to the method of bend resistanceperformance test, under the test condition of winding 100 turns on Φ 60mm reel, the additional attenuation induced by bending is less than 0.05dB at both 1550 nm and 1625 nm, under the test condition of winding 1turn on Φ 32 mm reel, the additional attenuation induced by bending isless than 0.5 dB at both 1550 nm and 1625 nm. The attenuation in thewhole 1530 nm˜1565 nm band is less than or equals to 0.23 dB/km. This isthe optimal transmission window at the present time, for is correspondsto the range in which the gain of EDFA is flat, and high bit rate DWDMtransmission may be carried out through it. In particular, because adepression structure is adopted in ΔClad3%, the cutoff wavelength islowered and less than 1310 nm, so that single mode transmission through1310 nm window may be performed simultaneously over the wide band nonzero dispersion-shifted fiber of the invention.

[0023] The invention adopts more complex refraction index profile torealize the equilibrium among dispersion, dispersion slope, effectivearea and attenuation performances. In addition, in combination with thecapability of precisely controlling the refractive index profile that ispeculiar to PCVD process, the designed performance can be realized withhigh efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a distribution graph showing schematically the relativerefractive index difference Δ% profile versus diameter in the firstembodiment of the invention;

[0025]FIG. 2 is a distribution graph showing schematically the relativerefractive index difference Δ% profile versus diameter in the secondembodiment of the invention;

[0026]FIG. 3 is a distribution graph showing schematically the relativerefractive index difference Δ% profile versus diameter in the thirdembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] In accordance with the invention, typically the core comprisesthree core segments, and the cladding comprises four cladding segments.The relative refractive index difference ΔCore1% of the first coresegment Core1 ranges approximately from 0.35% to 0.9%, and the diameterΦCore1 ranges approximately from 2.0 μm to 7.0 μm. The relativerefractive index difference ΔCore2% of the second core segment Core2ranges approximately from 0.25% to 0.65%, and the diameter ΦCore2 rangesapproximately from 3.0 μm to 8.0 μm. The relative refractive indexdifference ΔCore3% of the third core segment Core3 ranges approximatelyfrom 0.1% to 0.4%, and the diameter ΦCore3 ranges approximately from 4.0μm to 10.0 μm. The relative refractive index difference ΔClad1% of thefirst cladding segment Clad1 ranges approximately from −0.2% to 0.1%,and the diameter ΦClad1 ranges approximately from 8.0 μm to 16.0 μm. Therelative refractive index difference ΔClad2% of the second claddingsegment Clad2 ranges approximately from 0.1% to 0.4%, and the diameterΦClad2 ranges approximately from 12.0 μm to 25.0 μm. The relativerefractive index difference ΔClad3% of the third cladding segment Clad3ranges approximately from −0.2% to 0.2%, and the diameter ΦClad3 rangesapproximately from 19.0 μm to 30.0 μm. The fourth cladding segment is alayer of pure silica glass, and its refractive index is the refractiveindex of the pure silica glass n_(c).

[0028] As regards the preferable waveguide structure of the fiber of theinvention, both the relative refractive index difference ΔClad1% of thefirst cladding segment Clad1 and the relative refractive indexdifference ΔClad3% of the third cladding segment Clad3 are negative, andthe ranges of the parameters of the respective core segments andcladding segments are the follows: First core segment Core1: ΔCore1% isabout 0.42 ± 0.06 (0.36˜0.48) ΦCore1 is about 4.6 ± 0.7 μm (3.9˜5.3 μm)Second core segment Core2: ΔCore2% is about 0.35 ± 0.08 (0.27˜0.43)ΦCore2 is about 6.0 ± 1.0 μm (5.0˜7.0 μm) Third core segment Core3:ΔCore3% is about 0.28 ± 0.1 (0.18˜0.38) ΦCore3 is about 7.1 ± 1.5 μm(5.6˜8.6 μm) First cladding segment Clad1: ΔClad1% is about −0.08 ± 0.07(−0.01˜−0.15) ΦClad1 is about 12.5 ± 2.0 μm (10.5˜14.5 μm) Secondcladding segment Clad2: ΔClad2% is about 0.18 ± 0.07 (0.11˜0.25) ΦClad2is about 18.1 ± 2.0 μm (16.1˜20.1 μm) Third cladding segment Clad3:ΔClad3% is about −0.08 ± 0.07 (−0.01˜−0.15) ΦClad3 is about 27.0 ± 2.5μm (24.5˜29.5 μm)

[0029] Fourth cladding segment is a layer of pure silica glass, and itsrefractive index is the refractive index of the pure silica glass n_(c).

[0030] As compared with the former structure, more waveguide structuralparameters of the fiber, for example, ΔCore1%, ΦCore1, ΔCore2%, ΦCore2,ΔCore3%, ΦCore3, and the value of power α that determines the refractiveindex profile of Core1, can be adjusted. Therefore the design ofmultiple core segments has the capability of controlling theperformances of the fiber more precisely, and the dispersion, dispersionslope, effective area, and attenuation performances of the fiber can beequilibrated easily.

[0031] By adjusting the refractive index profile of the fiber, therequired values of dispersion, dispersion slope and larger effectivearea can be obtained, and said fiber possesses lower attenuation andexcellent bending performance. According to the invention, the totaldispersion of the fiber at 1550 nm is less than 0.060 ps/nm²·km, thezero-dispersion wavelength is less than 1420 nm, the effective arearanges from 55 μm² to 65 μm², the dispersion in the range of 1530nm˜1565 nm is 5.0˜12.0 ps/nm²·km, the attenuation at 1550 nm is lessthan or equals to 0.22 dB/km. According to the method of bend resistanceperformance test, under the test condition of winding 100 turns on Φ 60mm reel, the additional attenuation induced by bending is less than 0.05dB at both 1550 nm and 1625 nm, under the test condition of winding 1turn on Φ 32 mm reel, the additional attenuation induced by bending isless than 0.5 dB at both 1550 nm and 1625 nm. The attenuation in thewhole 1530 nm˜1565 nm band is less than or equals to 0.23 dB/km. This isthe optimal transmission window at the present time, for is correspondsto the range in which the gain of EDFA is flat, and high bit rate DWDMtransmission may be carried out through it. In particular, because adepression structure is adopted in ΔClad3%, the cutoff wavelength islowered and less than 1310 nm, so that single mode transmission through1310 nm window may be performed simultaneously over the wide band nonzero dispersion-shifted fiber of the invention.

Embodiment 1

[0032] The parameter set for relative refractive index differenceprofiles shown in FIG. 1 are listed as follows:

[0033] The parameters of the respective core segments are:

[0034] First core segment Core1:

[0035] ΔCore1% is about 0.64, ΦCore1 is about 3.0 μm

[0036] Second core segment Core2:

[0037] ΔCore2% is about 0.42, ΦCore2 is about 4.1 μm

[0038] Third core segment Core3:

[0039] ΔCore3% is about 0.21, ΦCore3 is about 7.5 μm

[0040] Fourth core segment Core4:

[0041] ΔCore4% is about 0.15, ΦCore4 is about 9.0 μm

[0042] The parameters of the respective cladding segments are:

[0043] First cladding segment Clad1:

[0044] ΔClad1% is about 0.04, ΦClad1 is about 15.0 μm

[0045] Second cladding segment Clad2:

[0046] ΔClad2% is about 0.25, ΦClad2 is about 21.0 μm

[0047] Third cladding segment Clad3:

[0048] ΔClad3% is about 0.04, ΦClad3 is about 27.0 μm

[0049] Fourth cladding segment Clad4:

[0050] ΔClad4% is about 0.02, ΦClad4 is about 31.0 μm

[0051] The outmost cladding segment is a pure silica glass layer.

[0052] The performances of the obtained fiber are the follows:

[0053] Effective area at 1550 nm: 56 μm²,

[0054] Zero dispersion wavelength: 1415 nm,

[0055] Dispersion at 1550 nm: 7.4 ps/nm·km,

[0056] Dispersion slope at 1550 nm: 0.054 ps/nm²·km,

[0057] Cutoff wavelength: 1530 nm,

[0058] Attenuation at 1550 nm: 0.20 dB/km,

[0059] Maximum additional attenuation induced at 1550 nm and 1625 nmfrom macro bending for 100 turns on Φ 60 mm reel: 0.001 dB,

[0060] Maximum additional attenuation induced from bending at 1550 nmand 1625 nm from macro bending for 1 turn on Φ 32 mm reel: 0.002 dB.

[0061] The dispersion slope of the fiber in Embodiment 1 is less than0.055 ps/nm²·km at 1550 nm, its zero-dispersion wavelength is shiftedout of S band, and it has excellent attenuation and bending performance,and its cutoff wavelength is lowered 200 to 400 nm after cabling. Therequirement of dense wavelength division multiplex in the S+C+L bandscan be fulfilled by such an optical fiber.

Embodiment 2

[0062] The parameter set for relative refractive index differenceprofiles shown in FIG. 2 are listed as follows:

[0063] The parameters of the respective core segments are:

[0064] First core segment Core1:

[0065] ΔCore1% is about 0.42, ΦCore1 is about 4.6 μm

[0066] Second core segment Core2:

[0067] ΔCore2% is about 0.35, ΦCore2 is about 6.0 μm

[0068] Third core segment Core3:

[0069] ΔCore3% is about 0.28, ΦCore3 is about 7.1 μm

[0070] The parameters of the respective cladding segments are:

[0071] First cladding segment Clad1:

[0072] ΔClad1% is about −0.10, ΦClad1 is about 11.5 μm

[0073] Second cladding segment Clad2:

[0074] ΔClad2% is about 0.18, ΦClad2 is about 16.2 μm

[0075] Third cladding segment Clad3:

[0076] ΔClad3% is about 0.02, ΦClad3 is about 29.0 μm

[0077] Fourth cladding segment is a pure silica glass layer.

[0078] The performances of the obtained fiber are the follows:

[0079] Effective area at 1550 nm: 64 μm²,

[0080] Zero-dispersion wavelength: 1395 nm,

[0081] Dispersion at 1550 nm: 7.4 ps/nm·km,

[0082] Dispersion slope at 1550 nm: 0.043 ps/nm²·km,

[0083] Cutoff wavelength: 1480 nm,

[0084] Attenuation at 1550 nm: 0.20 dB/km,

[0085] Maximum additional attenuation induced at 1550 nm and 1625 nmfrom macro bending for 100 turns on Φ 60 mm reel: 0.009 dB,

[0086] Maximum additional attenuation induced from bending at 1550 nmand 1625 nm from macro bending for 1 turn on Φ 32 mm reel: 0.014 dB.

[0087] The dispersion slope of the fiber in Embodiment 2 is less than0.050 ps/nm²·km at 1550 nm, its zero-dispersion wavelength is shiftedout of S band, and it has excellent attenuation and bending performance,and its cutoff wavelength is lowered 200 to 400 nm after cabling. Therequirement of dense wavelength division multiplex in the S+C+L bandscan be fulfilled by such a fiber.

Embodiment 3

[0088] The fiber of Embodiment 3 has two negative relative refractiveindex differences in its cladding segments. The parameter set for saidrelative refractive index difference profiles shown in FIG. 3 are listedas follows:

[0089] The parameters of the respective core segments are:

[0090] First core segment Core1:

[0091] ΔCore1% is about 0.42, ΦCore1 is about 4.6 μm

[0092] Second core segment Core2:

[0093] ΔCore2% is about 0.35, ΦCore2 is about 6.0 μm

[0094] Third core segment Core3:

[0095] ΔCore3% is about 0.28, ΦCore3 is about 7.1 μm

[0096] The parameters of the respective cladding segments are:

[0097] First cladding segment Clad1:

[0098] ΔClad1% is about −0.08, ΦClad1 is about 12.5 μm

[0099] Second cladding segment Clad2:

[0100] ΔClad2% is about 0.18, ΦClad2 is about 18.1 μm

[0101] Third cladding segment Clad3:

[0102] ΔClad3% is about −0.08, ΦClad3 is about 29.0 μm

[0103] Fourth cladding segment is a pure silica glass layer.

[0104] The performances of the obtained fiber are the follows:

[0105] Effective area at 1550 nm: 61 μm²,

[0106] Zero-dispersion wavelength: 1390 nm,

[0107] Dispersion at 1310 nm: −3.5 ps/nm·km,

[0108] Dispersion at 1550 nm: 8.3 ps/nm·km,

[0109] Dispersion slope at 1550 nm: 0.050 ps/nm²·km,

[0110] Cutoff wavelength: 1180 nm,

[0111] Attenuation at 1310 nm: 0.34 dB/km,

[0112] Attenuation at 1550 nm: 0.19 dB/km,

[0113] Maximum additional attenuation induced at 1550 nm and 1625 nmfrom macro bending for 100 turns on Φ 60 mm reel: 0.005 dB,

[0114] Maximum additional attenuation induced from bending at 1550 nmand 1625 nm from macro bending for 1 turn on Φ 32 mm reel: 0.011 dB.

[0115] The dispersion slope of the fiber in Embodiment 3 is less than0.055 ps/nm²·km at 1550 nm, its zero-dispersion wavelength is shiftedout of S band, and it has excellent attenuation and bending performance,and its cutoff wavelength is lowered 200 to 400 nm after cabling. Therequirement of dense wavelength division multiplex in the S+C+L bandscan be fulfilled by such a fiber. The smaller cutoff wavelength and thelower attenuation at 1310 nm make the traditional 1310 nm window can beused for single mode transmission. Thus a single mode transmissionthrough 1310 nm window is realized over a non-zero dispersion-shiftedfiber. In particular, because a depression structure is adopted inΔClad3%, the cutoff wavelength is lowered and less than 1310 nm, so thatsingle mode transmission through 1310 nm window may be performedsimultaneously over the wide band non-zero dispersion-shifted fiber ofthe invention. Adopting the standard test method, under the testcondition of winding 100 turns on Φ 60 mm reel, the additionalattenuation induced by bending is less than 0.01 dB at both 1550 nm and1625 nm, under the test condition of winding 1 turn on Φ 32 mm reel, theadditional attenuation induced by bending is less than 0.02 dB.

[0116] It can be seen by comparison of the aforesaid three embodimentsthat the refractive index profile can greatly affect the waveguideperformance. In particular, the refractive indices and diameters of therespective core segments can greatly affect the dispersion and effectivearea, i.e., the greater the relative index, the smaller the effectivearea. Because the segmenting core method is adopted in the design of thecore of the invention, the effective area and the dispersion can becontrolled precisely. The value of ΔClad1% can vary the dispersion slopeof the fiber, i.e., the smaller the relative value, the smaller thedispersion slope of the fiber. Though the value of ΔClad3% can affectthe effective area and the dispersion slope of the fiber, however, adepression structure is adopted in ΔClad3%, the cutoff wavelength islowered greatly, so that the possibility of single mode transmissionthrough 1310 nm window may be realized over a wide band non-zerodispersion-shifted fiber.

[0117] The previous description of the preferred embodiments is providedto enable any person skilled in the art to make or use the presentinvention. The various modifications to these embodiments will bereadily apparent to those skilled in the art, and the generic principlesdefined herein may be applied to other embodiments without the use ofinventive faculty. Thus, the present invention is not intended to belimited to the methods and apparatus shown herein but is to be accordedthe widest scope consistent with the claims set forth below.

1. A low dispersion slope dispersion-shifted single-mode fiber for largecapacity transmission comprising a core and a cladding is characterizedin that said core has three to five core segments having differentrefractive index profiles, and said cladding has four to six claddingsegments.
 2. The low dispersion slope dispersion-shifted single-modefiber according to claim 1, wherein the total dispersion slope of saidfiber at 1550 nm is less than 0.060 ps/nm²·km, the zero dispersionwavelength is less than 1420 nm, the effective area ranges from 55 μm²to 65 μm², and the dispersion in the region of 1530 nm˜1565 nm rangesfrom 5.0 ps/nm²·km to 12.0 ps/nm²·km.
 3. The low dispersion slopedispersion-shifted single-mode fiber according to claim 1, wherein saidcore has three core segments having different refractive index profiles,and said cladding has four cladding segments, and wherein the relativerefractive index difference ΔCore1% of the first core segment of saidcore ranges from 0.35% to 0.9%, its diameter ΦCore1 ranges approximatelyfrom 2.0 μm to 7.0 μm; the relative refractive index difference ΔCore2%of the second core segment Core2 ranges approximately from 0.25% to0.65%, and the diameter ΦCore2 ranges approximately from 3.0 μm to 8.0μm; the relative refractive index difference ΔCore3% of the third coresegment Core3 ranges approximately from 0.1% to 0.4%, and the diameterΦCore3 ranges approximately from 4.0 μm to 10.0 μm; the relativerefractive index difference ΔClad1% of the first cladding segment Clad1ranges approximately from −0.2% to 0.1%, and the diameter ΦClad1 rangesapproximately from 8.0 μm to 16.0 μm; the relative refractive indexdifference ΔClad2% of the second cladding segment Clad2 rangesapproximately from 0.1% to 0.4%, and the diameter ΦClad2 rangesapproximately from 12.0 μm to 25.0 μm; the relative refractive indexdifference ΔClad3% of the third cladding segment Clad3 rangesapproximately from −0.2% to 0.2%, and the diameter ΦClad3 rangesapproximately from 19.0 μm to 30.0 μm; the fourth cladding segment is alayer of pure silica glass, and its refractive index is the refractiveindex of the pure silica glass n_(c).
 4. The low dispersion slopedispersion-shifted single-mode fiber according to claim 3, wherein inthe preferable waveguide structure of the fiber, both the relativerefractive index difference ΔClad1% of said first cladding segment Clad1and the relative refractive index difference ΔClad3% of said thirdcladding segment Clad3 are negative.
 5. The low dispersion slopedispersion-shifted single-mode fiber according to claim 4, wherein theranges of the parameters of the respective core segments and claddingsegments are the follows: the parameters of said first core segmentCore1 are: ΔCore1% is about 0.42±0.06, ΦCore1 is about 4.6±0.7 μm; theparameters of said second core segment Core2 are: ΔCore2% is about0.35±0.08, ΦCore2 is about 6.0±1.0 μm; the parameters of said third coresegment Core3 are: ΔCore3% is about 0.28±0.1, ΦCore3 is about 7.1±1.5μm; the parameters of said first cladding segment Clad1 are: ΔClad1% isabout −0.08±0.07, ΦClad1 is about 12.5±2.0 μm; the parameters of saidsecond cladding segment Clad2 are: ΔClad2% is about 0.18±0.07, ΦClad2 isabout 18.1±2.0 μm; the parameters of said third cladding segment Clad3are: ΔClad3% is about −0.08±0.07, ΦClad3 is about 27.0±2.5 μm; and saidfourth cladding segment is a layer of pure silica glass, and itsrefractive index is the refractive index of the pure silica glass n_(c).6. The low dispersion slope dispersion-shifted single-mode fiberaccording to claim 1, wherein said core has four core segments havingdifferent refractive index profiles: the first core segment Core1, thesecond core segment Core2, the third core segment Core3, and the fourthcore segment Core4, and the parameters of said respective core segmentsare: the parameters of the first core segment Core1: ΔCore1% is about0.64, ΦCore1 is about 3.0 μm; the parameters of the second core segmentCore2: ΔCore2% is about 0.42, ΦCore2 is about 4.1 μm; the parameters ofthe third core segment Core3: ΔCore3% is about 0.21, ΦCore3 is about 7.5μm; and the parameters of the fourth core segment Core4: ΔCore4% isabout 0.15, ΦCore4 is about 9.0 μm, in which ΔCorei% is the relativerefractive index difference of the i^(th) core segment, Φcorei is thediameter of the i^(th) core segment, i=1, 2, 3,
 4. 7. The low dispersionslope dispersion-shifted single-mode fiber according to claim 3, whereinthe parameters of the respective core segments are: the parameters ofthe first core segment Core1 are: ΔCore1% is about 0.42, ΦCore1 is about4.6 μm; the parameters of the second core segment Core2 are: ΔCore2% isabout 0.35, ΦCore2 is about 6.0 μm; and the parameters of the third coresegment Core3 are: ΔCore3% is about 0.28, ΦCore3 is about 7.1 μm; andwherein the parameters of the respective cladding segments are: theparameters of the first cladding segment Clad1: ΔClad1% is about −0.10,ΦClad1 is about 11.5 μm; the parameters of the second cladding segmentClad2: ΔClad2% is about 0.18, ΦClad2 is about 16.2 μm; the parameters ofthe third cladding segment Clad3: ΔClad3% is about 0.02, ΦClad3 is about29.0 μm; and the fourth cladding segment is a pure silica glass layer.8. The low dispersion slope dispersion-shifted single-mode fiberaccording to claim 5, wherein the parameters of the respective coresegments are: the parameters of the first core segment Core1 are:ΔCore1% is about 0.42, ΦCore1 is about 4.6 μm; the parameters of thesecond core segment Core2 are: ΔCore2% is about 0.35, ΦCore2 is about6.0 μm; and the parameters of the third core segment Core3 are: ΔCore3%is about 0.28, ΦCore3 is about 7.1 μm; and wherein the parameters of therespective cladding segments are: the parameters of the first claddingsegment Clad1 are: ΔClad1% is about −0.08, ΦClad1 is about 12.5 μm; theparameters of the second cladding segment Clad2 are: ΔClad2% is about0.18, ΦClad2 is about 18.1 μm; the parameters of the third claddingsegment Clad3 are: ΔClad3% is about −0.08, ΦClad3 is about 29.0 μm; andthe fourth cladding segment is a pure silica glass layer.